Noise reducing

ABSTRACT

A module adapted for use in a noise reduction headset earcup has an enclosure having walls separating an interior of the enclosure from an exterior of the enclosure outside the earcup. There is a driver with a diaphragm. A port connects the interior and exterior. An acoustically resistive opening connects the interior and exterior in parallel with the port.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuing application of application Ser.No. 08/843,985 filed Apr. 17, 1997, for ACOUSTIC NOISE REDUCING of RomanSapiejewski.

BACKGROUND

[0002] For background, reference is made to U.S. Pat. Nos. 4,644,581,4,922,542 and 5,305,387.

[0003] It is an important object of the invention to provide an improvednoise reducing headset that may include active noise reduction.

BRIEF SUMMARY OF THE INVENTION

[0004] According to the invention, a module in a noise reduction headsetincludes an enclosure having walls. A driver is mounted in one of thewalls. A port and a resistive opening in parallel intercouples theinterior and exterior of the enclosure. The headset includes an earcupenclosing first and second cavities separated by a divider. The headsetfurther includes a circumaural sealing pad constructed and arranged toeffectively seal the first cavity to the head of a person.

[0005] In a specific aspect of the invention, for active noisereduction, a microphone is located in the first cavity adjacent to thedriver.

[0006] Other features, objects and advantages of the invention willbecome apparent from the following detailed description when read inconnection with the accompanying drawing in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0007]FIG. 1 is a plan view of a noise reduction headset;

[0008] FIGS. 2A-2C are diagrammatic cross-sectional views of earcupsemploying the invention;

[0009]FIGS. 3A and 3B are perspective views of a module according to theinvention;

[0010] FIGS. 4A-4C are cross-sectional views of alternate embodiments ofa module according to the invention;

[0011]FIG. 5 is a plot of driver response vs. frequency for the modulesof FIGS. 4A-4C;

[0012]FIG. 6 is a diagrammatic plan view of the open end of a cup in apassive headset according to the invention; and

[0013]FIG. 7 is a diagrammatic sectional view of the cup of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0014] With reference now to the drawing and more particularly to FIG.1, there is shown an active noise reduction headset according to theinvention. A headband 56 is attached to two earcup assemblies 58. Eachof the earcup assemblies 58 includes an earcup portion 50 and aconformable pad 54. The headband can be one of many types, includingheadbands in which the length of the headband or the position of theearcup assemblies on the headband can be adjusted. The connectionbetween the headband 56 and the earcup assemblies may allow foradjustment along one or more axes relative to the headband. In use, theheadband 56 holds the earcup assemblies 58 over the user's ears, eitherenclosing the ear (circumaural) or over the ear (supraural).

[0015] Referring to FIGS. 2A-2C, there are shown diagrammaticcross-sectional views of the earcup assembly 58. In FIG. 2A, earcupshell 50 encloses a front cavity 52. Conformable pads 54 seal againstthe side of the user's head so that they seal a user's ears from asubstantial portion of the ambient noise. Front cavity 52 enclosesactive noise reduction module 10. Active noise reduction module 10includes driver 18 which includes sound wave radiating diaphragm 21.Passing through earcup shell 50 are port 16 and acoustically resistiveopening 17 in parallel which will be described in more detail below. InFIGS. 2B and 2C, passageway 19 connects port 16 and resistive opening 17to the ambient environment. The dimensions of the passageway 19 are suchthat the passageway acts neither as a port nor a waveguide for soundwaves radiated by diaphragm 21; the acoustic effect is the same as ifthe port 16 and the resistive opening 17 both connect directly to theambient environment as in FIG. 2A. In front cavity 52 may be placeddamping material 53 (for example, open cell foam) to reduce resonancesin the front cavity and assist in passive attenuation. An embodiment asin FIGS. 2B and 2C is advantageous, because it allows flexibility in theplacement of the active noise reduction module, and it makes the activenoise reduction module 10 implementable in a variety of differentearcups with minimal modification to the earcup.

[0016] In operation, microphone 22 measures sound pressure. Circuitry(not shown) compares sound pressure measured by microphone 22 with soundpressure due to sound waves radiated by diaphragm 21 to detect ambientnoise, and transmits to driver 18 signals which cause diaphragm 21 toradiate sound patterns similar to the ambient noise, but out of phasewith ambient noise, thereby significantly attenuating it.

[0017] Referring to FIGS. 3A-3B, there are shown views of active noisereduction module 10. An enclosure 12 encloses a back cavity 14 (FIGS.4A-4C). Passing through a wall of enclosure 12 are port 16 andacoustically resistive opening 17. Mounted in a surface of enclosure 12is driver 18. Microphone 22 is mounted on the exterior of enclosure 12.In this embodiment, microphone 22 is mounted at a position approximatelyat the edge of diaphragm 21, with the pickup surface facing radiallyinwardly; that is, such that a line perpendicular to the pickup surfaceis approximately orthogonal to the axis 24 of driver 18.

[0018] In one embodiment of the invention, enclosure 12 is generallycylindrical, with driver 18 being approximately 42 mm in diameter andmounted in one of the planar surface of the cylinder. Back cavity 14enclosed by enclosure 12 has a volume of typically approximately 10 to20 cubic centimeters, and front cavity 52 typically has a volume ofabout 100-200 cubic centimeters. The acoustic mass of port 16 andcompliance of back cavity 14 are typically tuned to a frequency of about300 Hz. Acoustically resistive opening 16 provides an acousticresistance of about 1×167 ohms. Resistive opening 17 may be an opening17 a with an acoustically resistive covering 17 b, or may be an openingfilled with acoustically resistive material.

[0019] Referring now to FIGS. 4A-4C, there are shown the active noisereduction module 10 with certain elements omitted or modified to betterexplain the invention. FIGS. 4B-4D will be used below to explain theeffect of some of the features of the embodiment of FIG. 4A. In FIG. 4B,port 16 and resistive opening 17 are omitted. In FIG. 4C, resistiveopening 17 is omitted.

[0020] In the embodiment of FIG. 4A, the acoustic resistance of theresistive opening 18 connects back cavity 14 with ambient environment inparallel with the mass of the air in port 16.

[0021] Referring now to FIG. 5, there is shown plots of a computersimulation of the response of driver 18 as a function of frequency,illustrating the effect of various elements of the embodiment of FIG.3A. Curve 24 represents the response of driver 18 in the embodiment ofFIG. 4B. Curve 26 represents the response of driver 18 in the embodimentas shown in FIG. 4C. As compared with curve 24, curve 26 shows betterresponse at lower frequencies, but also has low output at the portresonance frequency, in this case 300 Hz. Curve 30 represents theresponse of the embodiment of FIG. 4A. As compared with curves 24, 26and 28, curve 30 shows smooth frequency response and improved responseat low frequencies.

[0022] An earcup according to the invention is advantageous overconventional earcups because the port and resistive path configurationallows active attenuation to be attained with a significantly smallerback cavity. This feature, in turn, allows for a given earcup size, alarger front cavity, which improves passive attenuation. The smoothfrequency response facilitates using simpler electronic circuitry, andcombined with the more efficient operation of the driver, allows forsignificantly reduced power consumption, a particular advantage inbattery-powered active noise reduction headsets.

[0023] Referring to FIGS. 6 and 7, there are shown diagrammatic plan andsectional views, respectively, of an earcup in a passive headsetaccording to the invention. Earcup shell 50′ carries driver 18′ coveredby damping foam layer 53′ typically ¼″ thick of 8-700Z foam formed withopenings 53A′ in the front cavity 52′ with circumaural cushion 54′constructed and arranged to effect a good seal against the side of theuser's head around the user's ears. Port 16′ and resistive opening 17′couple rear cavity 14′ to the ambient environment outside cup 50′. Thereare three openings 53A′ in damping foam layer 53′ as shown in FIG. 6,only one of which is visible in the sectional view of FIG. 7.

[0024] The invention provides passive attenuation by surrounding the earwith a cavity that is effectively sealed to the head. By using the port16′ and resistive opening 17′ structure according to the invention, rearcavity 14′ is effectively opened to the ambient region outside at lowfrequencies, but remains sealed at mid and high frequencies toeffectively increase low frequency output of driver 18′ with littleeffect on the overall passive attenuation. The arrangement of foam 53′with openings 53A′ positioned in front of the driver 18′ in front cavity52′ improves frequency response to provide passive equalization.

[0025] It is evident that those skilled in the art may now make numeroususes and modifications of and departures from the specific apparatus andtechniques herein disclosed without departing from the inventiveconcepts. Consequently, the invention is to be construed as embracingeach and every novel feature and novel combination of features presentin or possessed by the apparatus and techniques herein disclosed.

What is claimed is:
 1. A module adapted for use in a noise reductionheadset earcup comprising, an enclosure having walls separating aninterior of said enclosure characterized by compliance from an exteriorof said enclosure outside said earcup, a driver with a diaphragm, a portconnecting said interior and said exterior, said port having a mass thatcoacts with said compliance to establish a resonant circuit having aresonance at a resonant frequency, and an acoustically resistive openingconnecting said interior and said exterior in parallel with said port.2. A module in accordance with claim 1, further comprising a microphonehaving a pickup surface, said microphone mounted at approximately anouter edge of said diaphragm.
 3. A module in accordance with claim 2,wherein a pickup surface of said microphone is oriented perpendicularlyto an axis of said driver.
 4. A module in accordance with claim 2,wherein a pickup surface of said microphone faces radially inward.
 5. Amodule in accordance with claim 1, wherein said interior has a volume ofless than approximately 20 cc.
 6. An active noise reduction headsetcomprising, an earcup, enclosing a first cavity and a second cavityhaving compliance, said first cavity and said second cavity separated bya divider, a conformable pad constructed and arranged to seal saidearcup from a side of a head of a user, a driver having a diaphragmmounted in said divider, a port connecting said second cavity and theregion outside said earcup, said port having a mass that coacts with thesecond cavity compliance to establish a resonant circuit, and anacoustically resistive opening connecting said second cavity and theregion outside said earcup in parallel.
 7. An active noise reductionheadset in accordance with claim 6, further comprising a microphone insaid first cavity.
 8. An active noise reduction headset in accordancewith claim 7, wherein said microphone is mounted at approximately anouter edge of said diaphragm.
 9. An active noise reduction headset inaccordance with claim 6, wherein said divider comprises a wall of amodule, said module enclosing said second cavity, said module beingadapted to be removably integrated into said earcup in such a mannerthat said port and said acoustically resistive opening connect saidsecond cavity and said region through an opening in said earcup.